Ionic liquids and their use

ABSTRACT

Ionic compounds having a freezing point of no more than 50° C., formed by the reaction of at least one amine salt of the formula R 1 R 2 R 3 R 4 N + X −  (I) with at least one hydrated salt, which is a chloride, nitrate, sulphate or acetate of Li, Mg, Ca, Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd, Pb, Bi, La or Ce; wherein R 1 , R 2  and R 3  are each independently a C 1  to C 5  alkyl or a C 6  to C 10  cycloalkyl group, or wherein R 2  and R 3  taken together represent a C 4  to C 10  alkylene group, thereby forming with the N atom of formula (I) a 5 to 11 membered heterocyclic ring, and wherein R 4  is hydrogen, or phenyl, or C 1  to C 12  alkyl or cycloalkyl group, optionally substituted with at least one group selected from OH, Cl, Br, F, I, phenyl, NH 2 , CN, NO 2 , COOR 5 , CHO, COR 5  and OR 5 , wherein R 5  is a C 1  to C 10  alkyl or cycloalkyl group, and X −  is an anion capable of being complexed by the said hydrated salt. The compounds are useful as solvents, electrolytes, and catalysts, and have particular application in solvents/electrolytes for metal plating and electropolishing processes, in particular in chromium plating.

[0001] This invention relates to ionic compounds and methods for theirpreparation. In particular the invention relates to ionic compoundsformed between hydrated metal salts and amine salts, which are liquid atlow temperatures, and in particular which have a freezing point of 50°C. or less, and more preferably are liquid at or near to ambienttemperature (20° C.)

[0002] There is much current interest in the field of ionic liquids.Such systems, which are examples of molten salts, have a number ofinteresting and useful chemical properties, and have utility, forexample, as highly polar solvents for use in preparative chemistry, andas catalysts. They also have particular application in electrochemistry,for example in batteries, fuel cells, photovoltaic devices andelectrodeposition processes, for example in baths for the electroplatingof metals.

[0003] Ionic liquids have very low vapour pressure and thus, in contrastto many conventional solvents, produce virtually no hazardous vapours.They are therefore advantageous from a health, safety and environmentalpoint of view.

[0004] One such system which has been known for many years is thatformed from 1-ethyl-3-methylimidazolium chloride-aluminium chloride(EMIC-AlCl₃). This system is a thermally stable liquid between −100° C.and ca. 200° C., dependent on the molar ratio of EMIC to AlCl₃ utilised.

[0005] Such EMIC-AlCl₃ systems have been utilised extensively assolvents for various ionic reactions and as electrolytes, as described,for example in U.S. Pat. No. 5,525,567, FR-A-2611700, FR-A-2626572,WO95/21872, and EP-A-838447. There are a number of difficulties inutilising such compounds. These arise principally from their cost, andfrom their water sensitivity.

[0006] In recent years, other ionic compounds have been made which areliquid at relatively low temperatures. For example, U.S. Pat. No.4,764,440 discloses low temperature molten compositions, formed byreacting, for example, trimethylphenylammonium chloride with aluminiumtrichloride. The resulting ionic compound has a low freezing point(around −75° C.), but suffers from the same water sensitivity asEMIC-AlCl₃, because of the presence of aluminium trichloride.

[0007] Proposals have been made to utilise other metal halides, in placeof aluminium trichloride. For example, U.S. Pat. No. 5,731,101 disclosesthe use of iron and zinc halides as the anion portion of an ionic liquidcomposition. The cation portion is formed by an amine hydrohalide salt,of the formula R_(s)N.H.X (where X is halide). This reference indicates,however, that the aluminium compounds are preferred, and indeed containscomparative examples which indicate that it is not possible tosubstitute SnCl₄ for aluminium trichloride. Furthermore, it does notsuggest the use of quaternary ammonium compounds as cations.

[0008] FR-A-2757850 (equivalent to U.S. Pat. No. 5,892,124) disclosesliquid salts of the general formula Q⁺A⁻, wherein Q⁺ representsquaternary ammonium or phosphonium, and A⁻ represents various anionsincluding tetrachloroaluminate and trichlorozincate. It is suggestedthat such compounds are useful as vehicles for carrying out Diels-Alderreactions.

[0009] F. N. Jones J. Org. Chem., 1967, 32, 1667-8 describes an ioniccompound formed between Et₄N and SnCl₃ in a 1:1 molar ratio. The paperindicates that the solid and its solutions slowly decompose in air.

[0010] PCT/GB00/01090 describes liquid salts where the anion is a halidecomplex of zinc, iron or tin and the cation is chosen from certainspecific quaternary ammonium compounds. Such salts are liquid atrelatively low temperatures (i.e. below 60° C.), relatively inexpensive,and relatively water insensitive.

[0011] Because ionic liquids of this kind are generally water-sensitive,the conventional wisdom has been that all materials used in theirpreparation should be free of water, and in all of the above referencesthe metals salts employed are anhydrous or dried prior to use.

[0012] Surprisingly, however, we have now found that by forming theanion of an ionic compound from a hydrated metal salt and the cationfrom certain specific amine salts, it is possible to produce compoundswhich are liquid at low temperatures (i.e. 50° C. and below), relativelyinexpensive, and relatively water insensitive.

[0013] Accordingly, in a first aspect of the invention, there isprovided an ionic compound having a freezing point of no more than 50°C., formed by the reaction of at least one amine salt of the formula

R¹R²R³R⁴N⁺X⁻  (I)

[0014] with at least one hydrated salt, which is a chloride, nitrate,sulphate or acetate of Li, Mg, Ca, Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd, Sn,Pb, Bi, La or Ce; wherein R¹, R² and R³ are each independently a C₁ toC₅ alkyl or a C₆ to C₁₀ cycloalkyl group, or wherein R² and R³ takentogether represent a C₄ to C₁₀ alkylene group, thereby forming with theN atom of formula I a 5 to 11 membered heterocyclic ring,

[0015] and wherein R⁴ is hydrogen, or phenyl, or a C₁ to C₁₂ alkyl orcycloalkyl group, optionally substituted with at least one groupselected from OH, Cl, Br, F, I, phenyl, NH₂, CN, NO₂, COOR⁵, CHO, COR⁵and OR⁵, wherein R⁵ is a C₁ to C₁₀ alkyl or cycloalkyl group, and X⁻ isan anion capable of being complexed by the said hydrated salt.

[0016] In the amine salts (I) used in the preparation preferably R¹, R²,R³, are independently C₁ to C₅ alkyl or cycloalkyl groups, and morepreferably R¹, R², R³, are independently methyl, ethyl or butyl. It isparticularly preferred that R¹, R², R³, are each methyl, R¹, R², R³, areeach ethyl, or R¹, R², R³, are each butyl.

[0017] R⁴ is preferably a C₁ to C₁₀ alkyl or a cycloalkyl group,substituted with at least one group selected from OH, Cl, Br, F, I,phenyl, NH₂, CN, NO₂, COOR⁵, CHO, COR⁵ and OR⁵. The counterion X⁻ ofcompound (I) is preferably a halide, for example bromide or chloride.Specific examples of amine salts which have been found to be suitableare choline chloride, tetraethylammonium chloride, triethylammoniumchloride and benzyltrimethylammonium chloride.

[0018] The hydrated metal salt is preferably one of ZnCl₂.2H₂O,CaCl₂.6H₂O, MgCl₂.6H₂O, CrCl₃.6H₂O, CoCl₂.6H₂O, LaCl₃.6H₂O, CuCl₂.2H₂O,LiCl.5H₂O, Ca(NO₃)₂.4H₂O, Cr(NO₃)₃.9H₂O, Mn(NO₃)₂.4H₂O, Fe(NO₃)₃.9H₂O,Co(NO₃)₂.6H₂O, Ni(NO₃)₂.6H₂O, Cu(NO₃)₂.3H₂O, Li(NO₃).H₂O, Mg(NO₃)₂.6H₂O,La(NO₃)₃.6H₂O, Cd(NO₃)₂.4H₂O, Ce(NO₃)₃.6H₂O, Bi(NO₃)₃.5H₂O,Zn(NO₃)₂.4H₂O, Cd(OAc)₂.2H₂O, Pb(OAc)₂.3H₂O, or Cr₂(SO₄)3.15H₂O, and itis generally found that the most favourable freezing point is obtainedwhen the molar ratio of the amine salt to the hydrated metal salt isfrom 1:1 to 1:2.5, more preferably around 1:2.

[0019] The ionic compounds according to the invention may be preparedsimply by mixing together the amine salt (I), and the hydrated metalsalt. The reaction is generally endothermic, and is usually carried outby heating, for example to a temperature of 100° C. or more. Noadditional solvent is generally employed.

[0020] The ionic compounds according to the invention find particularapplication where a polar but non-aqueous solvent is required. Inparticular, they may be employed as inert media, for dissolving ionicspecies such as transition metal complexes and, either alone or aftercomplexing with other metal ions, as catalysts (particularly forcycloaddition reactions), or as chemical reagents.

[0021] They may be utilised for example as electrolytes inelectrochemical devices such as batteries or fuel cells, in photovoltaicor electrochromic devices, and as solvents for electrochemicalreactions, in particular for electrochemical deposition orelectro-refining. Electrodeposition from an ionic liquid containing amixture of hydrated metal salts may be preferred. In particular,compounds of the invention which incorporate chromium (III) ions havebeen found highly advantageous as solvents in the electroplating ofchromium. In such processes using the ionic compounds according to theinvention the addition of brightening agents and the use of potentialcycling have been found to improve the appearance of the coatingsobtained. Conventional chromium plating baths require the use of strongacids, which poses significant disposal problems, and the use of thecompounds of the invention enables such disposal difficulties to beminimised or eliminated.

[0022] The ionic compounds according to the invention also findapplication in electropolishing. For example, both aluminium andstainless steel can be polished using compounds according to theinvention. Stainless steels form the largest commercial application forelectropolishing and traditionally polishing baths contain mixturesbased on concentrated sulphuric and phosphoric acid. These are highlytoxic, and corrosive and prone to form toxic and corrosive “mists”during electropolishing, as a result of prodigious gas evolution due tothe high current densities used. A major advantage of the preferredelectropolishing processes according to the invention is that they aregenerally more environmentally friendly compared with the conventionalmethods. Additional advantages offered are that they can be performed atroom temperature and can operate with lower power consumption, whilstproviding bright reflective finishes comparable to traditionaltechniques. An additional advantage of the materials in accordance withthe invention is that when they are used in electrolytic baths, inparticular plating or electropolishing baths, hydrogen evolution issignificantly reduced, as compared with the acidic baths conventionallyemployed. This has a number of important consequences. First it resultsin very high current efficiency. Current efficiencies as high as 90% ormore can be obtained in favourable circumstances. Reduced hydrogenevolution is also advantageous from the safety standpoint and reducessignificantly the amount of hydrogen embrittlement that occurs in thesubstrate material during the electrochemical process. It also resultsin plated materials having an improved surface finish, with greatlydiminished micro-cracking than is the case with electroplatings producedby conventional methods. This in turn can improve the corrosionresistance of the coatings, and/or allow the use of coatings which arethinner, and yet provide comparable corrosion resistance to that ofconventional coatings, and thus are cheaper to produce, less consumptiveof raw materials, and more environmentally friendly.

[0023] In the following Examples, The freezing points of the hydratedsalt mixtures were all determined to be below 50° C. The conductivitiesof the hydrated salt mixtures were measured to determine their ionicnature. In each case, the conductivity was at least 10 microsiemens cm⁻¹at 10° C. above the freezing point of the material.

[0024] A number of preferred embodiments of the invention areillustrated in the following Examples, and with reference to theaccompanying Examples, in which:

[0025]FIG. 1 is a cyclic voltammagram of an ionic liquid formed from a2:1 molar ratio of chromium (III) chloride hexahydrate and cholinechloride;

[0026]FIG. 2 ia a schematic diagram of Hull cell used for chromiumdeposition; and

[0027]FIG. 3 is a voltage/current plot obtained in a chromium platingexperiment using an ionic liquid as used in FIG. 1.

EXAMPLE 1

[0028] A quaternary amine salt (choline chloride 1.40 g (0.01 mole)) wasadded to a hydrated metal salt (CrCl₃.6H₂O 5.33 g (0.02 mole)) in alaboratory test tube. The mixture was heated to a temperature of 120° C.for a period of 20 minutes. The product is a liquid which is initiallypurple in colour at 120° C. and a green liquid at 60° C.

EXAMPLES 2 to 15

[0029] Example 1 was repeated, using various hydrated chlorides as shownin Table 1, in a molar ratio of 1:2 (Amine salt:MCl_(x).yH₂O) as inExample 1 or in a molar ratio of 1:1. In each case, an ionic compoundwas prepared which had a freezing point of no more than 50° C. Freezingpoints (f.p.) are shown in Table 1. TABLE 1 MCl_(x) · yH₂O: MCl_(x) ·yH₂O: Choline Chloride (2:1) Choline Chloride (1:1) Hydrated f · p/Hydrated f · p/ Example Salt ° C. Example Salt ° C. 1 CrCl₃ · 6H₂O 4 9MgCl₂ · 6H₂O 16 2 CaCl₂ · 6H₂O 5 10 LiCl · 5H₂O 50 3 MgCl₂ · 6H₂O 10 11CrCl₃ · 6H₂O 10 4 CoCl₂ · 6H₂O 16 12 LaCl₃ · 6H₂O 14 5 LaCl₃ · 6H₂O 6 13CoCl₂ · 6H₂O 20 6 CuCl₂ · 2H₂O 48 14 CuCl₂ · 2H₂O 34 8 ZnCl₂ · 2H₂O 2015 ZnCl₂ · 2H₂O 20

EXAMPLES 16 to 40

[0030] Example 1 was repeated, using various hydrated nitrates as shownin Table 2, in a molar ratio of 1:2 (Amine salt:MCl_(x).yH₂O) as inExample 1 or in a molar ratio of 1:1. In each case, an ionic compoundwas prepared which had a freezing point of not higher than 50° C. TABLE2 M(NO₃)_(x).yH₂O: Choline M(NO₃)_(x).yH₂O: Choline Chloride (2:1)Chloride (1:1) Example Hydrated Salt Example Hydrated Salt 16Ca(NO₃)₂.4H₂O 30 Ca(NO₃)₂.4H₂O 17 Cr(NO₃)₃.9H₂O 31 Mn(NO₃)₂.4H₂O 18Mn(NO₃)₂.4H₂O 32 Co(NO₃)₂.6H₂O 19 Fe(NO₃)₃.9H_(z)O 33 Ni(NO₃)₂.6H₂O 20Co(NO₃)₂.6H₂O 34 Cu(NO₃)₂.3H₂O 21 Ni(NO₃)₂.6H₂O 35 Li(NO₃).H₂O 22Cu(NO₃)₂.3H₂O 36 Mg(NO₃)₂.6H₂O 23 Li(NO₃).H₂O 37 La(NO₃)₃.6H₂O 24Mg(NO₃)₂.6H₂O 38 Cd(NO₃)₂.4H₂O 25 La(NO₃)₃.6H₂O 39 Ce(NO₃)₃.6H₂O 26Cd(NO₃)₂.4H₂O 40 Bi(NO₃)₃.5H₂O 27 Ce(NO₃)₃.6H₂O 28 Bi(NO₃)₃.5H₂O 29Zn(NO₃)₂.4H₂O

EXAMPLES 41 to 46

[0031] Example 1 was repeated, using various hydrated salts (exceptchlorides or nitrates) as shown in Table 3, in a molar ratio of 1:2(Amine salt:MCl_(x).yH₂O) as in Example 1 or in a molar ratio of 1:1. Ineach case, an ionic compound was prepared which had a freezing point ofnot higher than 50° C. TABLE 3 MY_(x).yH₂O: Choline MY_(x).yH₂O: CholineChloride (2:1) Chloride (1:1) Example Hydrated Salt Example HydratedSalt 41 Cd(CH₃COO)₂.2H₂O 44 Cd(CH₃COO)₂.2H₂O 42 Pb(CH₃COO)₂.3H₂O 45Pb(CH₃COO)₂.3H₂O 43 Cr₂(SO₄)₃.15H₂O 46 Cr₂(SO₄)₃.15H₂O

EXAMPLES 47 to 49

[0032] Example 1 was repeated, using as the amine salttetraethylammonium chloride (47), triethylammonium chloride (48) andbenzyltrimethylammonium chloride (49), in molar proportion 1:2 (Aminesalt:MCl_(x).yH₂O).

EXAMPLE 50 Physical, Electrochemical and Chemical Properties of 2:1Chromium (III) Chloride Hexahydrate-Choline Chloride Hydrated SaltMixture

[0033] Below 80° C. the chromium hydrated salt mixture is a clear darkgreen liquid and at moderate temperatures (40° C. to 60° C.) it isreasonably fluid. When heated to 80° C. the liquid turns purple. It isthought that the colour change is due to the loss of water from the Crcoordination sphere.

[0034] The conductivity of the chromium hydrated salt mixture varieswith temperature. The temperature dependence was determined with the aidof a Jenway 4071 Conductivity Meter and Conductivity Probe. The probewas immersed in 2:1 chromium (III) chloride hexahydrate-choline chloridecontained in a sample tube which in turn was suspended in an oil bath.The hydrated salt mixture was heated to different temperatures and theresulting conductivity values were recorded. The results obtained areshown in Table 4. TABLE 4 Temperature/° C. Conductivity/mScm⁻¹ 20.4 0.1235.6 1.34 42.1 2.17 54.3 3.41 63.3 4.02 69.8 5.08 73.4 5.41 84.9 6.9296.4 8.21

[0035] The chemical composition of the 2:1 chromium (III) chloridehexahydrate-choline chloride hydrated salt mixture was studied usingmass spectrometry. The instrument used in this study was a KratosConcept Sector Mass Spectrometer equipped with negative ion fast ionbombardment (FAB). FAB mass spectra were obtained by introducing a smallamount of chromium hydrated salt mixture into the sample chamber andbombarding it with Xe atoms accelerated by a potential of 4 kV. Theresulting spectra revealed evidence for the existence of [CrCl₄]⁻ (m/z194).

EXAMPLE 51 Chromium Electrodeposition

[0036] A 2:1 chromium (III) chloride hexahydrate-choline chloridehydrated salt mixture (˜5 ml) was prepared, by the method of Example 1,and poured into an electrochemical cell held in an oil bath at 60° C.Voltammetry was performed using a 10 μm diameter platinum workingelectrode, a Pt wire counter-electrode and a chromium rod immersed inthe chromium hydrated salt mixture as the reference electrode. APGSTAT20 Potentiostat controlled by GPES software was used to carry outthe cyclic voltammetry. The results of this study are shown in FIG. 1.

[0037] The effect of current density on chromium deposition wasinvestigated using a Hull cell. The structure of the Hull cell enablesthe deposition of a metal at a range of current densities to be obtainedon a single cathode. A schematic diagram of the Hull cell employed isshown in FIG. 2.

[0038] To demonstrate chromium deposition a chromium (III)chloride-choline chloride hydrated salt mixture was prepared, by themethod of Example 1, and poured into a Hull cell as shown in FIG. 2,having dimensions

[0039] A=4.0 cm

[0040] B=5.0 cm

[0041] C=5.3 cm

[0042] D=1.3 cm

[0043] to a depth of approximately 1 cm.

[0044] The cathodic plate (substrate), 50 mm by 42 mm and 0.5 mm thick,was gently abraded with glass paper, cleaned with acetone and flameannealed. The cathodic plate was then placed inside the Hull cell alongedge C. The anodic plate, 40 mm by 40 mm and 1 mm thick, was cleaned ina similar way and then placed inside the Hull cell along edge A. TheHull cell was then suspended in a water bath set to a temperature so asto maintain the chromium hydrated salt mixture at 60° C. Chromiumdeposition was achieved by connecting the metal substrate and thecounter-electrode plates to the negative and positive terminalsrespectively of a Thurlby Thander power pack. In order accurately tomonitor the current flowing in the circuit, an ISO-TECH IDM 66 DigitalVoltmeter was connected in series. Chromium was plated onto nickel, mildsteel and aluminium substrates. In all of the experiments the depositiontime was 2 hours, after which time the substrates were removed from theHull cell, washed with acetone and dried. The effects of hydrated saltmixture composition and anode material (copper, nickel, graphite oraluminium) were investigated. The results obtained are described in thefollowing sections.

[0045] Chromium deposition onto nickel

[0046] Using a copper counter-electrode and a hydrated salt mixturecomposition of CrCl₃.6H₂O-choline chloride (2:1) a thick dark grey/greenhomogeneous deposit was obtained with current densities between 0.39 and0.25 mAcm⁻². A thinner greyer deposit was obtained with currentdensities between 0.25 and 0.19 mAcm⁻². Below 0.19 mAcm⁻² the chromiumdeposit was faint and non-homogenous. Numerous brightening agents wereadded to the hydrated salt mixtures to improve the surface finish of theelectrodeposited material. The addition of thiourea (0.75 wt %) to theelectrolyte produced a fainter non-homogenous deposit. Hydrogen was alsoproduced at the cathodic surface and this had a detrimental effect onthe quality of the chromium deposit. The addition of saccharin (0.75 wt%) had no significant effect on the appearance of the depositedchromium, however it should be noted that saccharin only partiallydissolves in the electrolyte. Similar chromium deposits were obtainedfrom the CrCl₃.6H₂O-choline chloride (2:1) electrolyte when nickel orgraphite were used as an anode in place of copper.

[0047] Chromium deposition onto mild steel

[0048] Chromium was successfully electroplated onto mild steel and ingeneral the deposits were thick and adherent. The major advantage of theprocess described in this report is that pre-treatment of mild steelsubstrates is not required. Using a nickel anode and an electrolytecomposition of CrCl₃.6H₂O-choline chloride (2:1) a thick dark green/greydeposit was obtained with current densities between 0.39 and 0.24mAcm⁻². A paler blue/grey deposit was obtained with current densitiesbetween 0.24 and 0.21 mAcm⁻². Between 0.21 and 0.18 mAcm⁻² the depositedchromium film was faint and non-homogenous. When the nickelcounter-electrode was replaced with either carbon or aluminium thechromium deposits obtained were fainter, thinner and less homogenous.Darker chromium deposits were obtained when a small amount of theCrCl₃.6H₂O in the electrolyte was substituted by LiCl or MgCl₂.6H₂O togive CrCl₃.6H₂O-LiCl-choline chloride (1.5:0.5:1) andCrCl₃.6H₂O-MgCl₂.6H₂O-choline chloride (1.8:0.2:1) respectively. With anickel counter-electrode and a current density between 0.33 and 0.21mAcm⁻² a smooth dark grey/brown adherent chromium deposit was obtainedfrom the CrCl₃.6H₂O-LiCl-choline chloride (1.5:0.5:1) electrolyte.

[0049] Several materials were tested as brighteners in the aboveexperiment. In each experiment, a nickel anode was used. Some of thematerials tested were immiscible with the electrolyte (vanillin—3.58 wt% and allyl urea—4.11 wt %) and had no effect on chromiumelectrodeposition. Nicotinic acid (4.11 wt %) and citric acid (1.82 wt%) dissolved in the electrolyte and the resulting chromium deposits wereslightly paler—however these materials led to hydrogen evolution at thesubstrate surface which in turn reduced the homogeneity of theelectrodeposited chromium film. Gelatin (3.58 wt %) only partiallydissolved in the CrCl₃.6H₂O-choline chloride (2:1) electrolyte at 60° C.and after approximately 10 minutes it caused the electrolyte to thickenand become less conductive. The chromium film obtained was predominantlygreen/grey but in places it was non-adherent. A similar deposit wasobtained when 2-mercaptobenzothiazole (2.34 wt %) was tested as abrightener.

[0050] We have found that the presence of specific additives, notgenerally recognised as brighteners, in 2:1 chromium (III) chloridehexahydrate-choline chloride can significantly brighten theelectrodeposit. For example when 10% of choline chloride is replaced bytetraethylammonium fluoride dihydrate or tetramethylammonium hydroxidepentahydrate thin semi-bright pale blue chromium deposits can beobtained. Approximately 6 ml of 2:1 chromium (III) chloridehexahydrate-[choline chloride (90%) tetraethylammonium fluoridedihydrate (10%)] was prepared by combining the reactants in a beaker andheating at 80° C. The green liquid was poured into an electrochemicalcell (internal diameter of 23 mm) held in an oil bath at 60° C. Mildsteel (50 mm by 10 mm and 1 mm thick), cleaned in the usual way, wasfixed to the inside edge of the cell opposite a nickel counterelectrode. The mild steel plate and counter-electrode were thenconnected to the negative and positive terminals respectively of aThurlby Thander power pack. Using current densities between 8 and 16mAcm⁻² and deposition times between 10 and 30 minutes semi-brightchromium deposits were obtained. The procedure was repeated usingapproximately 6 ml of 2:1 chromium (III) chloride hexahydrate-[cholinechloride (90%) tetramethylammonium hydroxide pentahydrate (10%)]. With acurrent density of 2 mAcm⁻² thin pale blue semi-bright homogenouschromium deposits were obtained after 30 minutes.

[0051] Similar electrodeposits were obtained when either potassiumdichromate (1.74 wt %) or potassium permanganate (1.41 wt %) were addedto the 2:1 chromium chloride hexahydrate-choline chloride hydrated saltmixture. Using the experimental set up described above, a currentdensity of 2 mAcm⁻² and a deposition time of 30 minutes, homogenoussemi-bright thin films of chromium were plated onto mild steel.

[0052] Chromium deposition onto aluminium

[0053] The CrCl₃.6H₂O-choline chloride (2:1) electrolyte could also beused to electrodeposit chromium onto an untreated aluminium surface.With a nickel counter-electrode and a current density between 0.47 and0.30 mAcm⁻² a grey/blue deposit was obtained. Between 0.30 and 0.25mAcm⁻² the deposit was slightly paler and greyer and between 0.25 and0.22 mAcm⁻² the chromium film became non-homogenous. As was the casewith electroplating chromium onto mild steel, darker deposits wereobtained when LiCl was incorporated into the electrolyte. With theelectrolyte composition CrCl₃.6H₂O-LiCl-choline chloride (2.25:0.75:1)and a current density between 0.47 and 0.28 mAcm⁻² a thick blackhomogenous deposit was obtained. Between 0.28 and 0.22 mAcm⁻² thedeposit was dark grey and less homogenous. Below 0.22 mAcm⁻² chromiumwas not electroplated onto the aluminium surface.

EXAMPLE 52 Potentiodynamic Electroplating Conditions

[0054] The above Examples show that chromium can be electroplated fromthe CrCl₃.6H₂O-choline chloride (2:1) electrolyte onto nickel, mildsteel and aluminium using potentiostatic conditions. The depositsobtained are thick, adherent and homogenous, but in general they lackbrightness. The surface finish of the chromium deposits was improvedusing a potentiodynamic technique rather than a potentiostatictechnique. The potential cycling regime was studied and optimised suchthat semi-bright chromium could be obtained. For these studiespotentiodynamic conditions were used with two parallel electrodes whichwere 17 mm apart. The cell has a depth of 3.5 cm.

[0055] For each experiment a Cr(III)-choline chloride hydrated saltmixture was prepared, by the method of Example 1, and poured into thecell to a depth of approximately 2.5 cm. The electrodes, 52×42×0.5 mmthick, were prepared by the same method reported above. The potentiallimits and the potential sweep rates for the potentiodynamic studieswere controlled using a PGSTAT20 Potentiostat. The potentiostat was usedin a ‘two electrode’ configuration. Chromium was plated onto mild steeland a variety of anode materials were tested.

[0056] Using a CrCl₃.6H₂O-choline chloride (1.8:1) mixture with a copperanode and a potential cycling range of 0V to −1.5 V at 20 mVs⁻¹ asemi-bright silver/blue chromium deposit was obtained after 28 cycles.When the cycling range was increased to 0 V to −1.8 V a slightly thickersilver grey deposit was obtained. A further increase in the cyclingrange to 0V to −2.1V produced a greyer deposit. Semi-bright silver/bluechromium films were also obtained from the CrCl₃.6H₂O-choline chloride(1.8:1) electrolyte with nickel and lead counter electrodes. Silver/greydeposits were obtained when aluminium, stainless steel and zinc wereused as the anode material. When mild steel or graphite were used asanodes the resulting chromium films were faint and non-homogenous.

[0057] Post-treatment and corrosion studies

[0058] The corrosion resistance afforded by chromium plated onto mildsteel using potentiodynamic conditions was assessed by holding thesamples approximately 5 cm above a boiling 10 wt % salt solution. Theunprotected regions began to rust after approximately 40 minutes andsoon after rust spots appeared in the chromium films. EDX analysis wasperformed on newly plated chromium films and the analyses showed thatchloride, from the electrolyte, had been incorporated into the metaldeposit. It is thought that the presence of chloride reduces thecrystallinity of the metal deposit and in the presence of moisture theseaid the breakdown of passivating films on the chromium surface. In orderto improve the corrosion resistance of the chromium films an additionalpost-treatment step was performed. This involved dipping the chromiumcoated sample, together with a counter electrode, into 0.1M KNO₃ andapplying a potential difference of 1.5V for 30 minutes thus allowing thechloride ions to be removed and the surface to be passivated. Chromiumfilms prepared from the CrCl₃.6H₂O-choline chloride (1.8:1) electrolytewith copper, nickel, lead or aluminium counter electrodes and apotential cycling range of 0 to −1.5 V were treated in this manner. Thecorrosion protection offered by these chromium deposits was excellent.The aforementioned corrosion test was repeated with various samples andthere was no obvious sign of corrosion after 24 hours—only slightstaining of the chromium films occurred.

[0059] An electrochemical technique was also used to determine theeffectiveness of chromium plating. A 1 mm diameter iron electrode waspolished with alumina paste down to 0.3 μm. Together with a polishedplatinum electrode and a saturated calomel reference electrode (SCE) theiron electrode was immersed in 50 ml of 0.1 M potassium nitratesolution. The potential of the iron electrode was swept from −1 V to 1 Vversus SCE at 20 mVs⁻¹. The scan (curve A) including the current arisingfrom iron oxidation is shown in FIG. 3.

[0060] The iron electrode was then cleaned, dried and immersed in 2:1chromium (III) chloride hexahydrate-choline chloride hydrated saltmixture contained in a boiling tube. Using a platinum electrode as acounter and a chromium rod as a reference, chromium was deposited ontothe iron at −0.25V versus chromium for 60 minutes. The deposition wasperformed at 60° C. The iron electrode was then removed from thehydrated salt mixture, washed with acetone, dried and re-immersed in0.1M potassium nitrate solution. As before the potential of the ironelectrode was swept from −1 V to 1 V versus SCE at 20 mVs⁻¹ (curve B).It can clearly be seen that chromium plating has reduced the corrosioncurrent by approximately 250 times.

EXAMPLE 53 Cobalt Electrodeposition

[0061] A 2:1 cobalt (II) chloride hexahydrate-choline chloride hydratedsalt mixture (˜5 ml) was prepared, by the method of Example 1, andpoured into an electrochemical cell held in an oil bath at 60° C.Voltammetry was performed using a platinum microelectrode (10 μmdiameter), a platinum counter-electrode and a cobalt referenceelectrode. An Autolab PGSTAT12 Potentiostat controlled by GPES softwarewas used to carry out the cyclic voltammetry.

[0062] To demonstrate cobalt deposition a 2:1 cobalt (II) chloridehexahydrate-choline chloride hydrated salt mixture (˜7 ml) was preparedand poured into an electrochemical cell (23 mm internal diameter) heldin an oil bath at 60° C. A mild steel plate, 50 mm by 10 mm and 1 mmthick, was gently abraded with glass paper, cleaned with acetone andflame annealed. The mild steel plate was then fixed to the inside edgeof the cell. A nickel plate of equal dimensions was cleaned in a similarway and also fixed to the inside edge of the cell opposite the mildsteel plate. Cobalt deposition was achieved by connecting the mild steeland nickel plates to the negative and positive terminals respectively ofa Thurlby Thander power pack respectively. A potential was applied andadjusted so as to maintain a current density of 2 mAcm⁻² for 30 minutes.An ISO-TECH IDM 66 Digital Voltmeter connected in series was used tomonitor the current. After 30 minutes the mild steel plate was removedfrom the cell, rinsed with acetone and dried. With a current density of2 mAcm⁻² a semi-bright grey/brown homogenous deposit was obtained.

EXAMPLE 54 Silver Deposition

[0063] A 2:1 tin (II) chloride dihydrate-choline chloride hydrated saltmixture (6.94 g) was prepared, by the method of example 1, and pouredinto an electrochemical cell held in an oil bath at 60° C. Silverchloride (0.3% wt)) was added to the clear colourless melt anddissolved. Voltammetry was performed using a platinum microelectrode (10μm diameter), a platinum counter-electrode and a tin referenceelectrode. An Autolab PGSTAT12 Potentiostat controlled by GPES softwarewas used to carry out the cyclic voltammetry. This technique could beused as the basis for an electrochromic device where a layer of silverwas deposited on a glass window.

[0064] To demonstrate silver deposition ITO glass (65 mm by 13 mm) and anickel counter-electrode (50 mm by 10 mm) were fixed to the inside edgeof the electrochemical cell opposite each other. Tin wire was dippedinto the ionic liquid and using the Autolab PGSTAT12 Potentiostat silverwas plated onto the ITO glass at 0.25 V versus tin. After 30 minutes adull grey semi-transparent film was obtained.

[0065] Silver has also been deposited from 2:1 lithium nitratehydrate-choline chloride. The hydrated salt mixture was prepared, by themethod of example 1, poured into an electrochemical cell to which silverchloride (0.3% wt) was added and dissolved, and the resulting liquid wassubjected to cyclic voltammetry using a platinum microelectrode and asilver wire as a reference electrode. To demonstrate silver depositionindium-tin oxide (ITO) glass (65 mm by 13 mm) and a nickelcounter-electrode (50 mm by 10 mm) were fixed to the inside edge of theelectrochemical cell opposite each other and connected to the negativeand positive terminals respectively of a Thurlby Thander power pack. Apotential difference of 2 volts was applied and after 20 minutes a dullgrey semi-transparent film was obtained.

EXAMPLE 55 Aluminium Electropolishing

[0066] An ionic liquid was prepared from a 2:1 mixture of zinc (II)nitrate tetrahydrate and choline chloride (˜5 ml), by the method ofExample 1. The material was cooled to 20° C. and poured into anelectrochemical cell. An aluminium electrode (52 mm by 7 mm and 1 mmthick) was cleaned, degreased and fixed to the inside edge of theelectrochemical cell. A carbon counter-electrode was cleaned with acloth moistened with acetone and fixed to the inside edge of theelectrochemical cell opposite the aluminium electrode. The aluminium andcarbon electrodes were connected to the positive and negative terminalsrespectively of a Thurlby Thander power pack. Various potentials wereapplied for 6 minutes and the initial current densities at the aluminiumelectrode were recorded to illustrate the current density/potentialrelationship for electropolishing aluminium in zinc (II) nitratetetrahydrate-choline chloride hydrated salt mixture. The resultsobtained are shown in Table 5 TABLE 5 Variation of current density withapplied potential and the effects on electropolishing. Applied voltageCurrent density Appearance of Al surface after 5 V At Al (mAcm⁻²)minutes 0 0 no change 1 0.2 ″ 2 1.1 ″ 3 3.5 ″ 4 8.8 ″ 5 17.2 Smootherand slightly brighter 6 27.5 Smooth and semi-bright 7 38.4 ″ 8 47 Smoothand ‘nearly’ bright 9 39 Smooth and very bright 10 41.4 ″ 11 43.4 ″ 1245.6 ″ 13 49 ″ 14 101 Etched and bright 15 122 ″ 16 141 Etched/pittedand semi-bright 17 160 Pitted and semi-bright 18 181 ″ 20 252 ″ 22 308Heavily pitted and dull grey 24 343 ″ 26 423 ″ 30 1397 ″

EXAMPLE 56 Stainless Steel Electropolishing

[0067] A 2:1 tin (II) chloride dihydrate-choline chloride hydrated saltmixture (˜6 ml) was prepared, by the method of Example 1, and pouredinto an electrochemical cell held in an oil bath at 40° C. Todemonstrate stainless steel electropolishing a stainless steel plate (50mm by 10 mm and 1 mm thick) was cleaned, degreased and fixed to theinside edge of the electrochemical cell. A stainless steelcounter-electrode (50 mm by 10 mm and 1 mm thick) was gently abradedwith glass paper, cleaned with acetone and flame annealed. The stainlesssteel counter-electrode was then fixed to the inside edge of theelectrochemical cell opposite the stainless steel plate.Electropolishing was achieved by connecting the stainless steelelectrodes to the positive and negative terminals of a Thurlby Thanderpower pack. A potential difference was applied across the 2:1 tin (II)chloride dihydrate-choline chloride electrolyte and adjusted so as tomaintain a current density of 65 mAcm⁻² for 6 minutes at the stainlesssteel anode. After 6 minutes the anode was removed from the cell, rinsedwith acetone and dried. The stainless steel plate was found to besmooth, bright and highly reflective. Scanning electron microscopy wasperformed and this revealed a highly ordered crystalline surfacenecessary for good reflectivity and enhanced corrosion resistance.

EXAMPLE 57 Battery

[0068] Two hydrated salt mixtures were prepared, 2:1 chromium(III)chloride hexahydrate-choline chloride and 2:1 copper(II) chloridedihydrate-choline chloride at 70° C. 2 ml of each were poured intoseparated compartments of a small glass cell. The compartments wereseparated by glass frit. The cell was suspended in an oil bath at 50° C.and zinc and copper strips (2 mm by 30 mm) were immersed in the chromiumand copper hydrated salt mixtures respectively. An ISO-TECH IDM66Digital Voltmeter was used to measure the resulting potentialdifference—the maximum recorded value was 1.04V.

EXAMPLES 58 to 67 Diels-Alder Reactions

[0069] General procedure for Diels-Alder reactions:

[0070] A mixture of diene (0.012 mol) and dienophile (0.012 mol) inZnCl₂.2H₂O:Choline chloride (2:1) (0.5 ml) hydrated salt mixture wasstirred (reaction time as given below) and pure cyclo-adduct wasseparated. For most of the reactions further purification was notnecessary but whenever appropriate flash column chromatography was usedfor further purification. In Examples 54 to 64, “rt” indicates 20° C.For each reaction investigated, the reaction scheme shown was followedemploying the procedure as noted in the reference quoted, and NMRchemical shifts (δ) were measured using a 250 MHz instrument.

EXAMPLE 58

[0071]

[0072] δ 9.67(s, 1H, CHO), 2.46(m, 1H, CHCHO), 2.12-1.81(m, 5H, 2×CH₂,CHH), 1.55(s, 3H, Me), 1.5(s, 3H, Me) and 1.53(m, 1H, CHH)

[0073] Ref: Odenkirk, W.; Rheingold, A. L.; Bosnich, B., J. Am. Chem.Soc., 1992, 114, 6392

[0074] After having separated out the cyclo-adduct and washed thehydrated salt mixture with hexane, the reaction was repeated in the samesample of hydrated salt mixture. The used hydrated salt mixture showedcomparable catalytic activity in five subsequent reactions.

EXAMPLE 59

[0075]

[0076] δ 9.46(s, 1H, CHO), 2.25-1.38(m, 6H, 3×CH₂), 1.62(s, 3H, Me),1.58(s, 3H, Me) and 1.01(s, 3H, Me).

[0077] Ref: Balwin, J. E. and Lusch, M. J., J. Org. Chem., 1979, 44.1923.

EXAMPLE 60

[0078]

[0079] δ 2.55(m, 1H, CHMe), 2.18(s, 3H, Me), 2.15-1.84(m, 4H, 2×CH₂),1.57(bs, 6H, 2×Me) and 1.57-1.42(m, 2H, CH₂).

[0080] Ref: Crabtree, R. H. and Davis, M. H., J. Org. Chem., 1986, 51,2655.

EXAMPLE 61

[0081]

[0082] (1,4) adduct: δ 9.69(d, 1H, J 1.15 Hz, CHO), 5.4(m, 1H, HC═C),2.46(m, 1H, CHCHO), 2.21-1.6(m, 6H, 3×CH2) and 1.65(s, 3H, Me).

[0083] Ref: Bonnesen, P. V.; Puckett, C. L.; Honeychuck, R. V. andHersh, W. H., J. Am. Chem. Soc., 1989, 111, 6070.

EXAMPLE 62

[0084]

[0085] (1,4) adduct: δ 9.67(s, 1H, CHO), 5.5(bs, 1H, HC═C), 2.6-1.6(m,6H, 3×CH₂), 1.83(s, 3H, Me) and 1.25(s, 3H, Me).

[0086] Ref: Balwin, J. E. and Lusch, M. J., J. Org. Chem., 1979, 44.1923.

EXAMPLE 63

[0087]

[0088] (1,4) adduct: δ 5.33(bs, 1H, HC═C), 2.54(m, 1H, CHCO), 2.19(s,3H, Me), 2.19-1.9(m, 4H, 2×CH₂), 1.64(s, 3H, Me) and 1.62(m, 2H, CH₂).

[0089] Ref: Bonnesen, P. V.; Puckett, C. L.; Honeychuck, R. V. andHersh, W. H., J. Am. Chem. Soc., 1989, 111, 6070.

EXAMPLE 64

[0090]

[0091] endo adduct: δ 9.45(d, 1H, J 1.3 Hz, CHO), 6.33(dt, 1H, J 0.9 and7.5 Hz, HC═C), 6.11(dt, 1H, J 0.9 and 7.5 Hz, HC═C), 2.94(m, 1H,aliphatic-H), 2.65(m, 1H, aliphatic-H), 2.54(m, 1H, aliphatic-H) and1.7-1.1(m, 6H, aliphatic-H).

[0092] Ref: Krantz, A. and Lin, C. Y., J. Am. Chem. Soc., 1973, 95,5662.

EXAMPLE 65

[0093]

[0094] Endo adduct: δ 9.42(s, 1H, CHO), 6.18(m, 1H, HC═), 5.96(m, 1H,HC═) and 1.93-1.2(m, 5H, 2×CH₂ and CH) with the peak of exo adduct at δ9.78(s, 1H, CHO).

[0095] Ref: Martin, A.; Reyes, B.; Jose, B. L.; Pedro, C. and Jose, J.L., Tetrahedron Lett., 1998, 39, 2013.

EXAMPLE 66

[0096]

[0097] Exo adduct: δ 9.67(s, 1H, CHO), 6.3(m, 1H, HC═), 6.08(m, 1H,HC═), 2.26(m, 1H, CH), 2.21(m, 1H, CH), 1.4-1.2(m, 3H, CH₂, CHH),0.98(s, 3H, Me) and 1.74(d, 1H, J 8.8 Hz, CHH) with the peak of endoadduct at δ 9.38(s, 1H, CHO).

[0098] Ref: Narasaka, K.; Inoue, M. and Okada, N., Chem. Lett., 1986,1109

EXAMPLE 67

[0099]

[0100] endo adduct: δ 6.14(m, 1H, HC═), 5.86)m, 1H, HC═), 3.25(bs, 1H,CH), 3.0(m, 1H, HCCHO), 2.88(bs, 1H, CH), 2.1(s, 3H, Me), 1.5-1.4(m, 3H,CH₂ and CHH) and 1.31(d, 1H, J 8.8 Hz, CHH).

[0101] Ref: Stork, G and Guthikonda, R. N., Tetrahedron Lett., 1972, 13,2755.

EXAMPLE 68

[0102] Radical polymerisation of a) styrene b) methyl methacrylate inthe presence of AIBN catalyst carried out in zinc chloride.2H₂O:cholinechloride:water (2:1) ionic liquid under the following conditions.

[0103] a)

[0104] 1. at 80 C, for 4.5 h

[0105] 2. at 80 C for 16 h

[0106] b)

[0107] 1. at 80 C, for 4.5 h

[0108] 2. at 80 C for 16 h

1. An ionic compound having a freezing point of no more than 50° C.,formed by the reaction of at least one amine salt of the formulaR¹R²R³R⁴N⁺X⁻  (I) with at least one hydrated salt, which is a chloride,nitrate, sulphate or acetate of Li, Mg, Ca, Cr, Mn, Fe, Co, Ni, Cu, Zn,Cd, Pb, Bi, La or Ce; wherein R¹, R² and R³ are each independently a C₁to C₅ alkyl or a C₆ to C₁₀ cycloalkyl group, or wherein R² and R³ takentogether represent a C₄ to C₁₀ alkylene group, thereby forming with theN atom of formula I a 5 to 11 membered heterocyclic ring, and wherein R⁴is hydrogen, or phenyl, or a C₁ to C₁₂ alkyl or cycloalkyl group,optionally substituted with at least one group selected from OH, Cl, Br,F, I, phenyl, NH₂, CN, NO₂, COOR⁵, CHO, COR⁵ and OR⁵, wherein R⁵ is a C₁to C₁₀ alkyl or cycloalkyl group, and X⁻ is an anion capable of beingcomplexed by the said hydrated salt.
 2. An ionic compound as claimed inclaim 1, wherein each of R¹, R², R³, independently is a C₁ to C₅ alkylor a cycloalkyl group.
 3. An ionic compound as claimed in claim 2,wherein each of R¹, R², R³, independently is methyl, ethyl or butyl. 4.An ionic compound as claimed in claim 3, wherein R¹, R², R³, are eachmethyl, R¹, R², R³, are each ethyl, or R¹, R², R³, are each butyl.
 5. Anionic compound as claimed in claim 4, wherein R¹, R², R³, and R⁴, areeach ethyl.
 6. An ionic compound as claimed in claim 4, wherein R¹, R²,R₃, are each ethyl, and R⁴ is hydrogen.
 7. An ionic compound as claimedin claim 1, wherein R⁴ is a C₁ to C₁₀ alkyl or a cycloalkyl group,substituted with at least one group selected from OH, Cl, Br, F, I,phenyl, NH₂, CN, NO₂, COOR⁵, CHO, COR⁵ and OR⁵, wherein R⁵ is as definedin claim
 1. 8. An ionic compound as claimed in claim 7, wherein R¹, R²,R³, are each methyl, and R⁴ is 2-hydroxyethyl.
 9. An ionic compound asclaimed in claim 7, wherein R¹, R², R³, are each methyl, and R⁴ isbenzyl.
 10. An ionic compound as claimed in any one of the precedingclaims, wherein X⁻ is Cl⁻ or Br⁻.
 11. An ionic compound as claimed inany one of the preceding claims, wherein the hydrated metal salt isZnCl₂.2H₂O, CaCl₂.6H₂O, MgCl₂.6H₂O, CrCl₃.6H₂O, CoCl₂.6H₂O, LaCl₃.6H₂O,CuCl₂.2H₂O, LiCl.5H₂O, Ca(NO₃)₂.4H₂O, Cr(NO₃)₃.9H₂O, Mn(NO₃)₂.4H₂O,Fe(NO₃)₃.9H₂O, Co(NO₃)₂.6H₂O, Ni(NO₃)₂.6H₂O, Cu(NO₃)₂.3H₂O, Li(NO₃).H₂O,Mg(NO₃)₂.6H₂O, La(NO₃)₃.6H₂O, Cd(NO₃)₂.4H₂O, Ce(NO₃)₃.6H₂O,Bi(NO₃)₃.5H₂O, Zn(NO₃)₂.4H₂O, Cd(OAc)₂.2H₂O, Pb(OAc)₂.3H₂O, orCr₂(SO₄)3.15H₂O.
 12. An ionic compound as claimed in any one of thepreceding claims, wherein the molar ratio of the amine salt to thehydrated metal salt is from 1:1 to 1:2.5.
 13. A method for preparing anionic compound, which method comprises reacting at least one amine saltof the formula R¹R²R³R⁴N⁺X⁻  (I) with at least one hydrated salt, whichis a chloride, nitrate, sulphate or acetate of Li, Mg, Ca, Cr, Mn, Fe,Co, Ni, Cu, Zn, Cd, Pb, Bi, La or Ce; wherein R¹, R² and R³ are eachindependently a C₁ to C₅ alkyl or a C₆ to C₁₀ cycloalkyl group, orwherein R² and R³ taken together represent a C₄ to C₁₀ alkylene group,thereby forming with the N atom of formula I a 5 to 11 memberedheterocyclic ring, and wherein R⁴ is hydrogen, or phenyl, or a C₁ to C₁₂alkyl or cycloalkyl group, optionally substituted with at least onegroup selected from OH, Cl, Br, F, I, phenyl, NH₂, CN, NO₂, COOR⁵, CHO,COR⁵ and OR⁵, wherein R⁵ is a C₁ to C₁₀ alkyl or cycloalkyl group, andX⁻ is an anion capable of being complexed by the said hydrated salt. 14.A method as claimed in claim 13, wherein the reaction is carried out byheating the compound of formula (I) with the said hydrated salt.
 15. Amethod as claimed in claim 13, in which molar ratio of the amine salt tothe hydrated metal salt is from 1:1 to 1:2.5.
 16. A method of carryingout an electrolytic reaction, which method comprises employing as asolvent for the electrolytic reaction an ionic compound as claimed inany one of claims 1 to
 13. 17. A method as claimed in claim 16, whereinthe reaction is an electroplating or an electropolishing reaction. 18.The use of an ionic compound as claimed in any one of claims 1 to 13, asa solvent, as an electrolyte or as a catalyst.
 19. The use of an ioniccompound as claimed in any one of claims 1 to 13, as an electrolyte inelectroplating, as an electrolyte in electropolishing, or as acycloaddition catalyst.
 20. A method of forming a solution of a solute,which method comprises dissolving the solute in an ionic compound havinga freezing point of no more than 50° C., formed by the reaction of atleast one amine salt of the formula R¹R²R³R⁴N⁺X⁻  (I) with at least onehydrated salt, which is a chloride, nitrate, sulphate or acetate of Li,Mg, Ca, Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd, Pb, Bi, La or Ce; wherein R¹, R²and R³ are each independently a C₁ to C₅ alkyl or a C₆ to C₁₀ cycloalkylgroup, or wherein R² and R³ taken together represent a C₄ to C₁₀alkylene group, thereby forming with the N atom of formula I a 5 to 11membered heterocyclic ring, and wherein R⁴ is hydrogen, or phenyl, or aC₁ to C₁₂ alkyl or cycloalkyl group, optionally substituted with atleast one group selected from OH, Cl, Br, F, I, phenyl, NH₂, CN, NO₂,COOR⁵, CHO, COR⁵ and OR⁵, wherein R⁵ is a C₁ to C₁₀ alkyl or cycloalkylgroup, and X⁻ is an anion capable of being complexed by the saidhydrated salt.